1. Field of the Invention
The present invention relates generally to gas turbine engines and, more specifically, to frames therein for supporting bearings and shafts.
2. Discussion of the Background Art
Gas turbine engines include one or more rotor shafts supported by bearings which, in turn, are supported by annular frames. Frames include an annular casing spaced radially outwardly from an annular hub, with a plurality of circumferentially spaced apart struts extending therebetween. The struts may be integrally formed with the casing and hub in a common casting, for example, or may be suitable bolted thereto. In either configuration, the overall frame must have suitable structural rigidity for supporting the rotor shaft to minimize deflections thereof during operation.
The struts have a hollow cross section through which pressurized cooling air passes and is routed into a hub. The pressurized air provides rotor purge for the high pressure and low pressure turbines through holes in the hub. The air also provides cooling for the strut and hub in addition to tubes contained within the struts which service the aft high pressure turbine (HPT) bearing. It is important that the pressurized air within the strut and hub not be lost due to leakage. If leakage occurs, the rotor cavity temperatures will be adversely affected.
One example of a bolted turbine frame assembly is a GE90 turbine center frame (TCF) which has an outer strut end connected to the outer case by eight bolts at each of the twelve strut ends. To minimize relative movement between the case and strut end, a shear bolt is used at each location which bounds off the hole in the case and strut end. To assure concentricity between the case hole and strut hole during manufacture, each strut is located relative to the case and each hole is machined through the case and strut in a single pass. The struts are then separated from the case and each previously machined through hole is used as a pilot to machine a counterbore feature for subsequent thread tapping and insert installation.
The struts are connected to the hub with a clevis and with 2 expandable bolts which provide a secure shear connection preventing any relative motion between the strut and hub. The struts have a hollow cross section through which pressurized air passes and is routed into the hub. The pressurized air provides rotor purge for the high pressure and low pressure turbines through holes in the hub box. The air also provides cooling for the strut and hub in addition to tubes contained within the hollow struts which service the aft high pressure turbine (HPT) bearing. It is important that the pressurized air within the strut and hub not be lost due to leakage. If leakage occurs, the rotor cavity temperatures will be adversely affected. Since the expandable bolts do not seal the strut to the hub it is desirable to prevent leakage of the pressurized air between the struts and the hub.
An annular turbine frame has ring disposed coaxially about an axial centerline axis and includes a plurality of circumferentially spaced apart ports. A plurality of circumferentially spaced apart struts are joined radially to the ring by clevises on the ring. Each strut has radially opposite first and second ends, and a through channel extending therebetween. Each of the channels is aligned with a corresponding one of the ports. Each of the ports has a port counterbore though a radially outer portion of the port forming a shoulder in the port. A seal is disposed within the port counterbore between the shoulder and the strut.